Reducing the surface reflection from the surfaces of optoelectronic and photovoltaic devices such as solar cells and photodetectors is of significant interest since these devices have many important applications. Solar cells are now the main power source used for satellites, and future plans for expanded telecommunications will require large amounts of power in space. Similarly, solar cells for the generation of electrical power on Earth are an important nonpolluting renewable energy source.
Currently, several techniques are used for reducing the surface reflection from semiconductor layers used in optoelectronic and photovoltaic devices. One such technique is the use of antireflection (AR) coatings. AR coatings, however, only reduce reflection to a limited extent and only in a narrow wavelength range.
Surface texturization processes have been used to reduce surface reflection from silicon, but have the drawback of increasing the junction and front surface areas, which increases the amount of dark or leakage current associated therewith. Moreover, most known surface texturizations are applicable primarily to silicon, and do not work well on compound semiconductors. In this regard, high angle V-grooves have been produced in the semiconductor surfaces to reduce reflection from the cells. A high angle V-groove reduces reflection from the cell by causing the light incident on one wall surface to reflect into the adjacent wall surface of the V-groove. High angle V-grooves, as noted above, have the drawback of increasing surface area which decreases the efficiency of a solar cell because of losses due to dark current. High angle V-grooves are also prone to shorting and junction shunting which also decreases the efficiency and processing yield. Furthermore, existing processes for forming high-angle V-grooves require a masking step to delineate the grooves during fabrication. This process adds to the cost and complexity of the fabrication process.
Solar cells are commonly encapsulated with a coverglass for protection from environmental degradation. One process proposes using light trapping in the coverglass to reduce reflection from the cell. This process requires the glass cover to be textured. The structure of the coverglass does not, however, allow the complete recovery of reflected light. Yet another structure proposes a system of grooves on the back of a silicon cell. This structure does not reduce front surface reflection, nor does it recover light reflected from front surface metallization.